The present invention generally relates to a battery cell construction, and more particularly relates to a positive cover for an alkaline battery cell.
Current alkaline batteries are typically constructed in the manner shown in FIGS. 1 and 2. Specifically, alkaline battery 10 includes a steel can 15 having a cylindrical shape with one open end. A metalized, plastic film label (not shown) is formed about the exterior surface of steel can 15 except for the ends of steel can 15. At a closed end 14 of steel can 15 is a positive cover 17 preferably formed of plated steel. A cathode 20, preferably formed of a mixture of manganese dioxide, graphite, potassium hydroxide solution, deionized water, and a TEFLON.TM. solution, is formed about the interior side surface of steel can 15. A separator 30, which is preferably formed of a non-woven fabric that prevents migration of any solid particles in the battery, is disposed about the interior surface of cathode 20. An electrolyte formed of potassium hydroxide, is disposed in the interior of separator 30. An anode 50, preferably formed of zinc powder, a gelling agent, and other additives, is disposed within an electrolyte in contact with a current collector 60, which may be formed of brass. Current collector 60 contacts a brass rivet 70 projecting through a nylon seal 71 formed at the open end of steel can 15 to prevent leakage of the active ingredients contained in steel can 15. Nylon seal 71 contacts a metal washer 72 and an inner cell cover 74, which is preferably formed of steel. A negative cover 75, which is preferably formed of a plated steel, is disposed in contact with inner cell cover 74 and brass rivet 70. Rivet 70 contacts current collector 60 through a hole formed in nylon seal 71. Negative cover 75 is electrically insulated from steel can 15 by nylon seal 71.
Positive cover 17 includes a protruding nub 18 at its center which forms the positive contact terminal of the battery. As shown in FIG. 1, positive cover 17 has a diameter that is substantially equal to the diameter of cylindrical steel can 15. Positive cover 17 contacts the closed end 14 of steel can 15 about its peripheral edge. Because the cell may bulge during storing, discharge, etc. and because positive cover 17 is rigid and inflexible, a gap 19 is provided between the inner surface of positive cover 17 and the exterior surface of closed end 14 of approximately 0.022 inch to allow for such bulging. The positive cover 17 can be fastened to the container by welds 42 after the cathode is rammed into place.
As shown in FIG. 2, positive cover 17 further includes a reinforcing rib 16, which protrudes outward about a peripheral edge of cover 17. In the assignee's current design, this reinforcing rib protrudes a little more than 0.042 inch from the outer surface of the closed end 14 of can 15. Further, the outer surface of positive contact terminal 18 extends an additional 0.090 inch from the outer surface of reinforcing rib 16 in the current design.
A primary goal in designing alkaline batteries is to increase the service performance of the cell. The service performance is the length of time for the cell to discharge under a given load to a specific voltage at which the cell is no longer useful for its intended purpose. One approach taken to increase service performance was to increase the interior volume of the cell in order to increase the amount of active materials within the cell. However, the commercial external size of the cell is fixed, thereby limiting the ability to increase the amount of active materials within the cell. For example, the cell length from the end of positive contact terminal 18 to the exterior surface of negative cover 75 is fixed by standards as well as the height of the protrusion that forms positive contact terminal 18.
In order to accommodate more active materials within the cell while maintaining the external size of the cell, the steel label and insulating paper tube of the original alkaline cell has been replaced with one made of thinner metalized plastic film. Thus, the steel can may be enlarged to provide a greater internal volume. By switching to a thinner plastic film label, the service performance of a typical alkaline cell was significantly increased. Another approach taken to increase the service performance of a cell is to provide for better utilization of the electrode materials. This approach is taken in U.S. Pat. No. 5,501,924 issued to Wendi Swierbut et al., which discloses utilizing tin dioxide as an additive to a cathode. Despite past increases in service performance, the need to find new ways to increase service performance remains the primary goal of cell designers.